1. Field of the Invention
The present invention relates to a cylinder inflow exhaust gas calculation system of an internal combustion engine amount and an intake passage inflow exhaust gas amount calculation system of an internal combustion engine.
2. Description of the Related Art
An internal combustion engine wherein an exhaust passage and intake passage of the internal combustion engine are connected through an exhaust gas recirculation passage and an exhaust gas flow rate control valve for controlling the flow rate of the exhaust gas flowing through the exhaust gas recirculation passage is arranged in the exhaust gas recirculation passage is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 8-128359. In this internal combustion engine, it is possible to introduce exhaust gas exhausted from a cylinder into the exhaust passage through this exhaust gas recirculation passage into the intake passage and thereby cause the exhaust gas to be recirculated into the cylinder. In an internal combustion recirculating the exhaust gas into a cylinder in this way, to determine the amount of fuel injection so that the air-fuel ratio becomes the target air-fuel ratio, the ratio of the exhaust gas in the amount of gas charged in the cylinder (that is, the EGR rate) is calculated.
In Japanese Unexamined Patent Publication (Kokai) No. 8-128359, the EGR rate at the time of steady state operation is found in advance in the form of a map and the EGR rate is found from this map at the time of steady state operation. Further, in Japanese Unexamined Patent Publication (Kokai) No. 8-128359, the EGR rate found from a map of the EGR rate at the time of steady state operation is utilized to estimate the EGR rate at the time of transient operation. Specifically, if the amount of exhaust gas passing through the exhaust gas flow rate control valve is called the “amount of passage gas”, the ratio of the amount of passage gas found relating to the actual opening degree of the exhaust gas flow rate control valve with respect to the amount of passage gas found relating to the target opening degree of the exhaust gas flow rate control valve is multiplied with the EGR rate at the time of steady state operation to find the EGR rate at the time of transient operation.
That is, if the amount of passage gas found relating to the target opening degree of the exhaust gas flow rate control valve is represented by Qt, the amount of passage gas found relating to the actual opening degree of the exhaust gas flow rate control valve is represented by Qa, and the EGR rate at the time of steady state operation is represented by Rc, in Japanese Unexamined Patent Publication (Kokai) No. 8-128359, the EGR rate at the time of transient operation is found from R=Rc·Qa/Qt. Further, in Japanese Unexamined Patent Publication (Kokai) No. 8-128359, note is taken of the fact that there is several minutes lag from when an instruction for changing the opening degree of the exhaust gas flow rate control valve is issued to when the opening degree of the exhaust gas flow rate control valve becomes the target opening degree and the EGR rate at the time of transient operation calculated exactly that amount of lag before is utilized as the EGR rate at the time of transient operation.
Summarizing the problems to be solved by the invention, in Japanese Unexamined Patent Publication (Kokai) No. 8-128359, the amount of the exhaust gas passing through the exhaust gas flow rate control valve is utilized to estimate the EGR rate at the time of transient operation based on the EGR rate at the time of steady state operation. The amount of exhaust gas charged in the cylinder itself is not directly found. Therefore, when estimating the amount of exhaust gas charged in the cylinder from the EGR rate at the time of transient operation, it can be said that the precision of the estimated value is not that high. Further, sometimes there is variation in the response of the exhaust gas flow rate control valve. In this case, the precision of calculation of the amount of gas itself passing through the exhaust gas flow rate control valve ends up becoming low.